Method for coating metal



W. S. RUSSELL METHOD FOR COATING METAL Dec. 1, 1970 5 Sheets-Sheet 1 Filed March 24, 1967 1970 w. s. RUSSELL 3, I

METHOD FOR COATING METAL Filed March 24, 196'? 5 Sheets-Sheet 2 Dec. 1, 1970 w. s. RUSSELL 3,544,388

METHOD FOR COATING METAL Filed March 24, 1967 5 Sheets-Sheet 5 Dec. 1, 1970 w, s, RUSSELL I 3,544,388

METHOD FOR COATING METAL Filed March 24, 1967 5 Sheets-Sheet 4 D c. 1, 19 0 w. s. RUSSELL 3,544,388

METHOD FOR COATING METAL Filed March 24, 1967 5 Sheets-Sheet 5 Patented Dec. 1, 1970 3,544,388 METHOD FOR COATING METAL William S. Russell, Warren, Mich., assignor to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York Filed Mar. 24, 1967, Ser. No. 625,743 Int. Cl. C23f 7/00 US. Cl. 148-614 3 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for treating metal sheet and strip in an immersion type process with a chemical conversion type coating solution to form a protective and/ or paint base coating on the metal surface. The sheet or strip is introduced into a coating zone wherein a chemical conversion coating solution is flowed in contact with the metal surface. The amount of coating produced on the surface is controlled by varying the size of the coating zone. The apparatus for accomplishing this has a coating chamber which may be increased or decreased in length. The chamber itself may be telescoping, Or have a longitudinally movable end wall, or have a series of folding, transverse partitions or be made up of a series of separate, connecting coating zones, each with its own coating solution inlet.

This invention relates to an improved process, and the apparatus for use therein, for producing a coating on metal surfaces and more particularly it relates to a method and apparatus for applying chemical conversion coatings to metallic sheet and strip.

In the art of applying chemical conversion coatings to metal surfaces the coating compositions are conventionally brought into contact with the surface to be coated either by spraying the coated material on the metal surface or by immersing the metal surfaces to be coated in a body of the coating solution. Although both coating techniques have been widely used in the past, both are subject to some disadvantages, particularly when used for coating metallic sheet and/or strip. Although the spray application of the conversion coating materials may be carried out in a relatively short period of time, with fairly good control over the coating Weights obtained on the surfaces treated, it is sometimes difficult to obtain relatively heavy coating weights, e.g., in excess of about 30 to 50 milligrams per square foot, by this method. Additionally, depending upon the type of conversion coating material being used, clogging of the spray nozzles may also occur, thus necessitating shutting down a line while the nozzles are cleaned or replaced. Moreover, it has sometimes been found to be difficult to obtain a satisfactory sprayed coating on the bottom, as well as the top of sheet or strip material. Accordingly, for many applications, particularly where both the top and bottom of sheet and strip material are to be coated, immersion coating techniques may be preferable.

In immersion coating processes, however, a relatively large body of the coating solution is normally required in order to provide sufiicient contact between the coating solution and the metal surface being treated. Additionally, the coating rate with such techniques is appreciably longer than that required with spray applications, thus, further adding to the amount of coating solution and the size of the coating tank required to obtain the desired coating weights. Moreover, because the accelerating components of the coating solution are more rapidly depleted than the coating components, generally only about 20 to 30% of the coating components can be utilized before replacement or replenishment of the coating solution is necessary. This, coupled with the time required to obtain the desired coating weights by this method, adds greatly to the operating cost of such a process.

It is, therefore, an object of the present invention to provide an improved immersion type coating process, which process may be carried out in an appreciably shorter period of time with a much smaller volume of coating solution then has heretofore been possible.

Another object of the present invention is to provide an improved immersion coating process in which the weight of coating obtained on the surface being treated is more easily controlled.

A further object of the present invention is to provide improved apparatus of the immersion coating type for carrying out the process as has been described hereinabove.

These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

In the drawings which are attached hereto and form a part hereof, FIG. 1 is a schematic, sectional side elevation, of one form of the apparatus of the present invention;

FIG. 2 is a schematic, sectional side elevation, of a modified form of the present apparatus;

FIG. 3 is a schematic, sectional plan view of the apparatus shown in FIG. 2;

FIG. 4 is a schematic, sectional side elevation, of another modification of the present apparatus; and

FIG. 5 is a schematic, sectional side elevation, of yet another modified form of the apparatus of the present invention.

Pursuant to the above objects, the present invention includes a method for forming a chemical conversion coating on metal sheet and strip which comprises passing the metal surface to be coated through a coating zone containing a liquid chemical conversion coating composition, flowing fresh coating composition through the coating zone in contact with the metal surface to be coated, maintaining said surface in contact with said coating composition in the coating zone for a period sufiicient to form the desired chemical conversion coating thereon and controlling the amount of coating produced on said surface by varying the size of the coating zone through Which the metal surface is passed.

More specifically, in the practice of the method of the present invention, metallic sheet or strip which is to be coated is passed through a coating zone which contains a liquid, chemical conversion coating composition. The sheet or strip to be coated may be of any suitable metal which may be given a chemical conversion coating, such as ferrous metal, aluminum, zinc, magnesium, including alloys which are predominantly of these metals, and the like.

The coating composition in the coating zone may be any of the various chemical conversion coating materials, i.e., coating compositions wherein there is a reaction of the coating material and the metal surface being coated, and include those compositions which produce on the metal surface a phosphate, chromate, oxalate, sulfide, or oxide coatings. Typically, the conversion coating composition may be aqueous solutions of alkali metal or ammonium phosphates, zinc phosphate, iron phosphates, manganese phosphates, oxalic acid, or oxalates, phosphoric acid, chromic acid, and the like, as are known to those in the art. In addition to the coating components which have heretofore been listed, these conversion coating compositions generally also contain one or more accelerating or activating components which act to enhance the quality of the coating which is produced. These include simple and complex fluoride ions, nitrate ions, nitrite ions, chlo rate ions, molybdate ions, nickel ions, bromate ions, halide ions and the like.

The coating solutions used are formulated so as to contain the solution components; i.e., the coating and accelerating components, in the amounts and relative ratios which will provide the desired optimum coating results. Obviously, the exact quantities and ratios used will vary in each instance, depending uponthe particular chemical coating solution which is used. Exemplary of typical coating solutions which may be used are those which contain the following components in amounts within the ranges indicated:

Percent by weight Component (A) CIO 0.05-2 HF 0.01-1 (B) C130 (105-2 H PO 0.01-5 HF 0.01-1 (C) Zn(H PO 0.1-5 H P 0.02-1.6 4 0.044.5 (D) NaH2PO .06-3 Na HPO .04-2 NaClO O.15 (E) H C 'O 0.2-5 aCl 0.2-4 NaHF 0.2-3

N32S203 0- (F) 0.1-5 H PO 0.02-l.6 Zn(NO L -Q 0.4-4.5 ZnSiF 0.1-4 Ni(NO 0.1-3 (G) C10 L. 0.1-1 Na MoO 0.03-0-3 V HF Q. 0.030.3

It is to be appreciated that in the above solutions, as is known to those in the art, the hosphate, chromium and oxalate materials are the coating components of the solution, whereas the nitrate and chlorate materials, as well as otherssuch as molybdates, halides, bromates, nickel, silico fluorides and the like are the accelerating components.

suitable sourcesof the coating and/or accelerating components which make up the solution. For example, the hexavalent chromium ions in the solutions may be provided by using chromic acid, alkali metal chromates and dichromates; the phosphate ions may be provided by the use of phosphoric acid, zinc phosphates, alkali metal phosphates; the fluoride ion accelerator may be added as hydrogen fluoride (hydrofluoric acid); alkali metal bifluorides,e.g., sodium bifluoride, fluoroboric acid, fluosilicic acid, oxalate ions may beadded as oxalic acid; while the nitrate may be added as zinc or alkali metal nitrate and the chlorates as the alkali metal chlorates, or the like. Inasmuch as these coating solutions are desirably aqueous solutions, the materials used are desirablysoluble, or at least dispersable, in water, so as to provide the desired solution. In selecting water-soluble salts to supply the various coating and accelerating components, such as the alkali metal and ammonium salts and the like, care should be taken that other extraneous ions are not introduced into the coating solution which may be detrimental either to the coating solution or to the coating produced on the metal surfaces treated. Accordingly, it may be preferably to formulate these coating solutions using chromic acid as the source of hexavalent chromium ions; phosphoric acid or zinc phosphate as the source of phosphate ions; oxalic acid as the source of oxalate ions; hydrofluoric acid, as the source of active fluorine in the composition; and the like.

As has been noted hereinabove, the consumption of the accelerating ions in these conversion coating solutions takes place more rapidly than the consumption of the coating ions in the solution. Thus, when the accelerating The coating solutions may be formulated using various ions in these solutions have been depleted to a level so that there is an insufficient quantity of the accelerator in the solution to eifect the formation of a coating having the desired quality, in a-reasonable coating time, the coating ions have generally been depleted to the extent of only about 20 to 30% of the total content in the coating solu tion. Accordingly, in the method of the present invention, fresh coating solution is passed through the coating zone and contacted with the surface to be coated at a rate such that the concentration of the accelerating ions in the solution is maintained at a substantially constant level. Desirably, the fresh coating solution is introduced into and removed from the coating zone ina minimum amount of at least 50 milliliters of solution for each square foot of metal surface being treated in the zone, although in some instances, lesser amounts may also satisfactorily be used. Preferably, the amount of coating solution which is passed through the coating zone is within the range of about 200 to 300 milliliters of solution per each square foot of metal being treated. As will be apparent to those skilled in the art, the actual flow rate of the coating solution through the coating zone will depend upon the rate at which the metal surface to be treated is passed through the coating zone as well as the size, i.e., width of the metal sheet or strip. Thus, for example, where a five foot wide strip of metal is being treated, which strip is traveling at a rate of about feet per minute, considering both the top and bottom surfaces of the strip, a total of about 1000 square feet of metal .per minute is passing through the coating zone. At a preferred flow of about 250 milliliters per square foot, the actual flow rate of the coating composition through the coating zone would be about 250,000 milliliters per minute or about 64 gallons per minute.

The metal surface to be coated is maintained in contact with the chemical conversion coating solution for a period sufficient to efiect the formation of the desired coating on the metal surface. Obviously, of course, the time available for the metal surface to be in contact with the coating solution in the coating zone will depend upon the size of the coating zone and the rate at which the metal is passed therethrough. It has been found that because fresh coating solution is continually flowing in contact with the metal surface as it passes through the coating zone, so that the accelerating ions in the coating solution are constantly maintained at a substantially even, high level, the desired coating is formed on the metal surface being treated in appreciably shorter periods of time than have heretofore been possible. Typical contact times which have been found to be suitable are within the range of about 1 to 20 seconds, with contact times within the range of about 2 to 8 seconds being preferred.

The coating zone through which the metal to be coated is passed in contact with the coating solution, may be of any suitable configuration which has means for varying the size of the coating zone. Desirably, the coating zone is a simple, box-like structure which is relatively shallow but which has suflicient depth to permit a metallic sheet or strip to be completely immersed in the coating solution as it passes through the coating zoneJPreferably, the entrance to and exit from the coating zone are disposed in the opposing end walls of the coating zone so that the sheet or strip to be coated passes through these end walls, rather than being introduced through the top of the coating zone. Any suitable means for adjusting the relative size of the coating zone may be used. For example, the coating zone may be formed with one or more telescoping sections, so that the zone may be lengthened or shortened to increase or decrease its size. As an alternative, the fluid or coating solution inlet to the coating zone may be positioned adjacent the end of the coating zone from which the metal treated is removed and the coating zone may be provided with a movable partition or panel which is transverse of the coating zone and through which the metal sheet or strip to be coated is passed. Thus, by moving this position either closer to or further away from the end of the coating zone through which the coated metal is discharged, the coating zone can be either shortened or lengthened. As another alternative, the coating zone may be provided with a number of transverse, folding panels or partitions, each provided with a suitable opening through which the sheet or strip to be treated is passed. The effective length of such a coating zone may then be changed by raising different of these panels, the other panels remaining folded flat against the bottom of the coating zone. In still another alternative configuration, the coating zone may be provided with several permanent transverse panels or partitions, through which the metal sheet or strip is passed, so that the coating zone is divided into a number of consecutive sections. In such a configuration, a coating solution inlet and outlet would be provided in each of these sections. It is believed that these and other means for effecting the change in the size of the coating zone will be apparent to those in the art.

It has been found that by changing the size of the coating zone, an excellent control on the coating Weight produced on the metal surfaces being treated can be obtained and these coatings are effected in an appreciably shorter period of time than has heretofore been possible in immersion type process. Thus, for any given rate of travel for the sheet or strip to be coated, by changing the size of that portion of the coating zone which contains the coating composition, the effective time that the metal surface is in contact with the coating solutions will be changed, thus changing the amount or weight of coating which is formed on the metal surface. Thus, for example, if a coating weight of milligrams per square foot is being obtained on a metal strip which is traveling at the rate of 100 feet per minute when there is coating solution in the entire coating zone, by reducing the portion of the coating zone which contains the coating solution to onehalf that of the full coating zone, a coating weight of only 25 milligrams per square foot can be obtained without having to change the speed at which the stri is traveling. This is, therefore, a much simplier and more easily used method of controlling the coating weight, which makes it possible to maintain a substantially constant operation in the coating line.

In some instances, it has been found to be desirable if the metal surface to be coated is conditioned prior to being introduced into the coating solution so that the reaction of the coating solution with the metal surface will take place more quickly. Although various treatments may be used to effect this conditioning, in general, it has been found to be preferable to pass the metal sheet or strip between one or more sets of squeegee rolls prior to bringing it into contact with the coating solution. By thus treating the metal surface to be coated, it is found that there is frequently an appreciable reduction in the time required to form the desired coating on the surface.

In addition to the coating process which has been set forth hereinabove, the present invention also includes novel apparatus for carrying out this process. This apparatus comprises a coating chamber, means for introducing a surface to be coated into said chamber, means for removing the thus-coated surface from said chamber, means for introducing a coating composition into said coating chamber, means for removing the coating composition from said coating chamber, said latter two means acting in conjunction to provide a sufficient amount of coating composition in said chamber as to maintain the surface to be coated substantially immersed in the coating composition, and adjusting means for varying the size of said coating chamber, whereby the length of time the surface to be coated is immersed in the coating composition while in the coating chamber may be changed.

More specifically, the apparatus of the present invention comprises a coating chamber, which coating chamber may be of any suitable configuration. Desirably, the coating chamber has a box-like construction, having a relatively shallow depth with respect to its width and length. This coating chamber is provided with means for introducing a surface to be coated, such as metallic sheet or strip, into the coating chamber, wherein it is brought into contact with a suitable coating composition.

In many instances, it has further been found to be desirable if the means for introducing the surfaces to be coated into the coating chamber are provided in the end walls of the chamber so that the sheet or strip may move in a substantially horizontal direction, rather than being dipped into the coating chamber from above. This may be accomplished by providing suitable apertures or slots in the end walls of the coating chamber, which slots may be provided with flexible sealing strips through which the metallic sheet or strip passes and which will prevent or at least minimize the flow of coating solution out of the coating chamber through the slots. Generally, however, such sealing strips are not required. It is to be appreciated, that the surfaces to be coated may also be introduced into the coating chamber from the top, as for example, by passing it under a suitable bar or roller in the bottom of the coating chamber which serves to maintain the metallic strip under the surface of the coating solution in the chamber.

The coating chamber is provided with means whereby the effective length of the chamber which contains the coated solution may be varied, thus varying the length of time that the metal surface is in contact with the coating solution, for any given rate of speed of the metallic sheet or strip which is being treated. Similarly, of course, by varying the length of the coating chamber as the speed of the strip varies, the coating time, and hence the coating weight obtained can be maintained constant. Various means may be provided whereby this variation in the coating chamber may be obtained. For example, the coating chamber itself may be formed of one or more telescoping sections whereby the chamber may be shortened or lengthened. Alternatively, the coating chamber may be provided with a transverse wall or partition which is movable longitudinally in the chamber, thereby changing the length of the chamber which will contain the coating solution. As a further alternative, the coating chamber may be provided with one or more folding walls or partitions which may be raised or lowered to change the length of the chamber which contains the coating solution. In each of these configurations, the apparatus is desirably provided with a solution inlet which is adjacent the exit end of the coating chamber, through which the coating solution may be introduced from a suitable supply tank, and a solution drain which is adjacent the entrance end of the coating chamber, through which the coating solution may be removed and returned to the supply tank. As still another alternative configuration, the coating chamber may be provided with a series of separate coating zones, each of which is provided with a solution inlet and drain. In such configuration, the effective coating length of the coating chamber is varied depending upon the number of the separate coating zones which are utilized.

In some instances, it has also been found to be desirable if the coating apparatus of the present invention is provided with a set of opposed squeegee rolls which are positioned adjacent the entrance and exit ends of the coated chamber. It has been found that the squeegee rolls which are adjacent the entrance end of the coating chamber help to condition the metal surface to be coated, thus making it possible to effect the coating operation in a shorter period of time, while the rolls adjacent the exit end of the coating chamber remove any excess coating solution which is carried out of the coating chamber by the metal surface.

The coating apparatus of the present invention may be positioned with respect to the metal surface to be coated in any convenient manner. As has been noted hereinabove, the placement of the coating chamber is preferably such that the metallic surface to be treated will pass through the coating chamber with substantially no deviation from a horizontal plane. Accordingly, suitable support members'may be provided for the coating chamber which will maintain it in the desired position, with regard to the metal surface to be coated. Additionally, it has been found desirable in many instances to provide a suitable drain tank which is positioned under the coating chamber, so as to recover any of the coating solution which may be carried out in the coating chamber by the metal surface itself and return it to the solution tank, from which it is recirculated back into the coating chamber. Generally, it has been found that the solution drained from the coating chamber, itself, may also discharge directly into such a drain tank so that piping or conduits from the drain to. the solution tank are not required.

Referring now to the drawings which are attached hereto and form a part hereof, FIG. 1 is a schematic, sectional side view of one form of the coating apparatus of the present invention. As shown in this figure, the coating chamber 2 is formed by the end walls 4 and 6 and the top and bottom members 8 and 10. Within the coating chamber 2 is a movable wall or partition 3, which partition extends across the width of the coating chamber and is longitudinally movable within the chamber. The end walls 4 and 6 and the movable wall 3 are provided with slots or apertures 5, 7 and 9, respectively, through which the metallic strip 1, to be coated, is passed in traveling through the coating chamber 2.

A coating solution supply tank 12 is provided which is positioned below the coating chamber 2 from which coating solution'is removed through the conduit 15 by the pump 13 and pumped through the inlet conduit 14 into the coating chamber. The inlet conduit 14 is positioned adjacent the exit end of the coating chamber 2 and a drain pipe 16 is positioned adjacent the entrance end of the coating chamber, through which the coating solution is removed after passing through the coating chamber. A drain tank 11 is positioned below the coating chamber 2 so as to receive coating solution from'the drain pipe 16, as well as any coating solution which may pass through the slots and 7 in the end walls 4 and 6 of the coating chamber. The drain tank 11 is further positioned so as to return this coating solution to the solution supply tank 12. Additionally, a pair of squeegee rolls 17 and 18 are posi tioned adjacent the entrance and exit ends, respectively, of the coating chamber 2.

In operation, the movable partition 3 is positioned within the coating chamber 2 to provide a coating zone of appropriate length, depending upon the amount of coating which is desired on the metal surface to be treated and the rate at which the metal is to be passed through the coating chamber. The position of the movable partition 3 may be at various places along the'length of the coating chamber 2, for example, as is shown by the dotted lines at 3' and 3". After the movable partition 3 has been suitably located, coating solution from the supply tank 12 is introduced into the coating chamber 2 through the inlet line 14 by the pump 13. The coating solution is pumped at a rate so as to substantially fill the coating zone formed by the end wall 6 and the movable wall 3 in the coating chamber, the coating solution flowing out through the slot 9 in the movable wall 3, through the drain pipe 16 and returned to the supply tank 12 by means of the drain tank 11. The metal strip 1 to be coated, passes through the slot 5 in the end wall 4 and through the slot 9 in the movable wall 3 into contact with the coating solution. The metal strip 1 then passes through the slot 7 in the end wall 6 and out of the coating chamber 2. As the strip 1 leaves the coating chamber 2, it passes through the squeegee rolls 18 which remove any unreacted coating solution which still remains on the strip, which coating solution passes into the drain tank 11 and is returned to the solution supply tank 12. By changing the position of the movable wall 3 within the coating chamber 2, as for example by positioning it as at 3' or 3", the length of that portion of the coating chamber which contains the coating solution will be either shortened or lengthened so that for a given rate of speed of the metal strip through the coating chamber, the length of time the strip is in contact with the coating solution will be similarly changed, thus producing a different weight of coating on the metal surface.

Referring now to FIGS. 2 and 3, these show a schematic, sectional side elevation and plan view, respectively, of an alternative configuration of the apparatus of the present invention. This apparatus, like that shown in FIG. 1, comprises a coating chamber 2 formed by the end walls 4 and 6 and the top and bottom members 8 and 10. In this configuration, however, the coating chamber 2 is formed into three separate coating zones, 19, 20 and 21, by the two intermediate walls 22. Each of these coating zones is provided with a coating solution inlet 24 and a solution drain 25. Additionally, the end walls 4 and 6 and the two intermediate walls 22 are each provided with a hole or slot, 5, 7 and 23, respectively, through which the'metal strip 1 is passed in being introduced into the coating chamber 2 and brought into contact with the chemical coating solution. Additionally, the apparatus, like that shown in FIG. 1, is provided with a drain tank 11, a coating solution supply tank 12, a pump 13 by means of which the coating solution is supplied through the conduits 15, 14, 32 and 33 to the solution inlets 24 in the three coating zones. Two sets of squeegee rolls, 17 and 18, positioned adjacent the entrance and exit ends of the coating zone are also provided. It will be appreciated that, in this configuration of the present apparatus, variations in the coating weights which is applied to the metal strip being treated may be obtained by varying the number of the separate coating zones in the coating chamber which are filled wtih coating solutions. Thus, in the apparatus shown in FIGS. 2 and 3, either 1, 2 or 3 of the coating zones may contain coating solutions depending upon the coating weight which is desired. It is to be further appreciated, of course, that the number of such coating zones which are provided in the appratus may be varied, as desired, thus providing more flexibility in the operation of the apparatus.

Referring now to FIG. 4, this figure is a schematic, sectional side view of another variation of the apparatus of the present invention. In this configuration, like that shown in the previous figures, there is a coating chamber 2 formed by the end walls 4, 6 and the top and bottom members 8 and 10. With this coating chamber, however, there are a series of intermediate wall members 26, which wall members are secured to the top member 8 and extend into the coating chamber, terminating short of strip 1, which passes through the chamber. A series of second wall members 27 are also provided, which latter members may be folded so as to lay substantially fiat along the bottom member 10 of the coating chamber or may be raised to form, with the upper wall members 26, a transverse partition across the coating chamber 2. The end walls 4 and 6, are provided with a slot, 5 and 7, respectively, through which the metallic strip 1 is passed in going through the coating chamber in contact with the coating solution. Additionally, the upper wall members 26 and the folding wall members 27 are joined together so as to form a slot through which the strip passes. The coating chamber 2 is provided with an inlet pipe 14 through which the coating solution is pumped from the coating tank 12 through the conduit 15 by means of the pump 13. Additionally, an outlet or drain 16 is provided in the opposite end of the coating chamber2 through which the coating solution is removed to the drain tank 11 and returned to the solution coating tank 12. Additionally, as in the previous figures, squeegee rolls 17 and 18 are pro vided adjacent the entrance and exit ends of the coating chamber 2. It will be appreciated that in this configuration, the efiective length of the coating chamber 2, which contains the coating solution, may be varied depending upon which of the folding intermediate walls 27 is raised so as to form a transverse wall or partition across the coating chamber. Although in this figure only three folding intermediate partitions have been shown, this number may be varied so as to provide additional variations in the length of the coating chamber which will be used.

Referring now to FIG. 5, this figure is a schematic, sectional side view of yet another variation of the apparatus of the present invention. As shown in this figure, the coating apparatus comprises a coating chamber 2 having the end walls 4 and 6. This coating chamber is formed of two telescoping sections 28v and 29, each of which have the top and bottom members 30 and 31. As in the previous configuration, slots or apertures 5 and 7, respectively, are provided in the end walls 4 and 6 and a coating solution inlet conduit 14 is provided adjacent the exit end of the coating chamber 2, while a solution drain 16 is positioned adjacent the entrance end of the coating chamber. Coating solution is supplied to the chamber from the solution supply tank 12 by means of the conduit 15 and the pump 13 and the excess solution is returned through the drain tank 11 t the supply tank. Squeegee rolls 17 and 18 are also provided adjacent to the entrance and exit ends of the coating chamber 2, respectively. In this configuration, the metal strip 1 to be coated is introduced into the coating chamber 2 through the slots and 7 and passes through this chamber in contact with the coating solution which is contained therein. By moving the two telescoping sections 28 and 29 of the coating chamber 2, the effective length of this chamber may be varied, thus varying the length of time that the metal strip 1 is in contact with the coating solution within the coating chamber and, hence, the coating weight which is produced on the strip.

From the above, it will be appreciated that various configurations may be used in the apparatus of the present invention to provide a coating chamber in which the elfective length of the coating solution containing portion of the chamber may be varied so as to control the amount of coating material which is obtained on the metal surface being treated. It is believed that other similar variations will be apparent to those in the art which will be suitable for accomplishing substantially the same results. It has been found that when the coating chambers are provided with such means, greater utilization of the coating solution is obtained, so that in many instances, the volume of the coating chamber need only be /5 to /2 as large as for conventional immersion apparatus.

EXAMPLE 1 A metal coating solution was prepared containing the following components in the amounts indicated:

Components: Percent by weight CI'O3 0.5 K Fe(CN) 0.04 HF 0.12 Water Balance Using the apparatus as shown in FIG. 1 this coating solution, at a temperature of about 43 was flowed through the coating chamber at a rate of gallons/minute, the portion of the coating chamber containing the coating solution having a length of 4 feet. 6" wide aluminum metal strip 3003 alloy was passed through the coating chamber at a rate of feet/minute, so that the strip was in contact with the coating solution for a period of 2 seconds. In this manner, there was formed on the metal strip a chromate coating having a weight of 20 milligrams/ square foot, which coating was found to have excellent protective and paint base qualities when subjected to the standard testing procedures.

EXAMPLE 2 The procedure of Example 1 was repeated with the exception that the coating solution used contained the following components in the amounts indicated:

Components: Percent by weight N3-H2PO4 0.6 Na HPO 0.4 NaClO 0.9 Water Balance This coating solution, at a temperature of about 63 C. was flowed through the coating chamber of the apparatus at a rate of 2 gallons/minute, the portion of the coating chamber containing the coating solution having a length of 3 feet. A' cold rolled steel metal strip was passed through the coating chamber and the solution therein at a rate of 40 feet/minute thus providing a total contact time between the metal surface and the coating solution of 4.5 seconds and a coating weight of 42 milligrams/ square feet was obtained on the metal strip. The thusobtained coating was found to have excellent paint-base properties.

EXAMPLE 3 The procedure of Example 1 was repeated with the exception that the coating solution used contained the following components in the amounts indicated:

Components: Percent by weight ZH(H2PO4)Z 1.1 H PO 0.2 Zn 2 2. 1 ZnSiF 0.4 Ni( N0 2 0.6 Water Balance This coating solution, at a temperature of 60 C., was flowed through the coating chamber of the apparatus at a rate of 6 gallons/minute, the portion of the coating chamber containing the coating solution having a length of 12 feet. A hot dipped galvanized strip was passed through the coating chamber and the solution therein at a rate of feet/ minute, thus providing a total contact time between the metal and the solution of 5 seconds. A coating weight of 120 milligrams/square foot was obtained which had excellent protective and paint-base properties.

EXAMPLE 4 The procedure of Example 3 was repeated, using the same solution, but at a temperature of about 66 C. A cold rolled steel strip was passed through the coating chamber at a rate of 75 feet/minute, providing a contact time of 10 seconds. A coating weight of 100 milligrams/ square foot was obtained, which coating had excellent protective and paint-base properties.

EXAMPLE 5 The procedure of Example 1 was repeated with the exception that the coating solution used contained the following components in the amounts indicated:

Components: Percent by weight CrO HF 0.03 Na MoO 0.07 Water Balance This coating solution, at a temperature of 54 C., was flowed through the coating chamber of the apparatus at a rate of 40 gallons/minute, the portion of the coating chamber containing the coating solution having a length of 12 feet. A hot dipped galvanized strip and aluminum strip were both passed through the coating chamber and the solution therein at a rate of 60 feet/minute, thus providing a total contact time between the metal and the solution of 20 seconds. A coating weight of 14 milligrams/ square foot was produced on the aluminum and a coating weight of 22 milligrams/ square foot was produced on the galvanized strip. In each case, the coating formed had excellent protective and paint-base properties.

While there have been described various embodiments of the invention, the compositions, methods and apparatus described are not intended to be understood as limiting the scope of the invention as it is realized that changes therewithin are possible, and it is further intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. A method for forming a chemical conversion coating on metal sheet and strip which comprises passing the metal surface is be coated through a coating zone containing a liquid chemical conversion coating composition, flowing fresh coating composition through the coating zone in contact with the metal surface to be coated, the fresh coating composition being flowed through the coating zone in an amount of at least 50 milliliters of composition per minute for each square foot of metal surface being treated I 12 w in the coating zone, maintaining the metal surface in contact with the coating composition in the coating zone for a period of time within the range of about 1 to. 20 seconds, said period of time being sufficient to completely form the desired chemical conversion coating on the metal surface 'within the coating zone and controlling the amount of coating produced on the surface by varying the size of the coating zone through which the metal surface is passed. a

2. The method as claimed in claim 1 wherein the coating produced on the metal surface is a coating selected from the group consisting of phosphate, oxalate, oxide and sulfide coatings.

3. The method as claimed in claim 2 wherein the metal surface to be treated is maintained in a substantially horizontal plane as it is introduced into and pressed through the coating zone.

References Cited UNITED STATES PATENTS 2,111,853 3/1938 Fourness et a1. 118-405 X 2,254,216 9/1941 Gordon (1486.15) 2,875,111 2/1959 Wilkinson et a1. 1486.15 3,144,361 8/1964 Klinghoffer 148-615 X 3,396,699 8/1968 Beebe et al. 118-405 X RALPH S. KENDALL, Primary Examiner US. Cl. X.R. 

